The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, various circuits and methods were utilized to control synchronous rectifiers in power supply systems. Usually, the control methods depended on the operating mode and the type of power supply system. Flyback type power supply systems usually required complex control circuits. In a flyback converter, the synchronous rectifier typically was in the secondary side of the power supply system and the switching power supply controller was in the primary side of the power supply system. One method utilized a fixed frequency clock to predict the time in which the synchronous rectifier should be enabled or disabled. An example of such a flyback system was disclosed in U.S. pat. No. 6,418,039 issued to Franco Lentini et al on Jul. 9, 2002. Complicated circuitry was required to implement the control. The complicated circuitry increased the system cost. Additionally, it was difficult to accurately predict the proper time to enable and disable the synchronous rectifier, thus, the operation was inefficient.
Accordingly, it is desirable to have a control method and circuit that accurately controls a secondary side synchronous rectifier, that does not require complicated circuitry, and that has low cost.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor.